1. Field of the Invention
The present invention relates to a gallium-nitride (GaN) based light-emitting diode (LED) structure, and in particular to the gallium-nitride (GaN) based light-emitting diode with high reverse withstanding voltage and high electrostatic discharge (ESD) capabilities.
2. The Prior Arts
A number of image displaying devices are currently utilized, including a cathode ray tube (CRT) display, a liquid crystal display (LCD), and a light-emitting diode (LED) based display. Usually, the liquid crystal display is suitable for displaying dynamic images, while the display made of LED is suitable for displaying static images.
In the field of light-emitting diodes, the gallium-nitride (GaN) based light-emitting diode is the focus of research and development of the industry in recent years. Its main feature lies in that it can be made to emit lights of various colors by adjusting its material compositions. The field of its application has been expanded tremendously, due to the significant breakthrough and development of the technology in enhancing its light illumination and light emitting efficiency.
In general, the indium-gallium-nitride (InGaN)/gallium-nitride (GaN) multi-quantum well (MQW) LED is used in the prior art as the light emitting device, and it has been widely utilized in the various functions and applications of static display, for example, in addition to being used in the electronic clocks and watches, it can be utilized in the application of various display screens and advertisement panels/billboards, etc.
When it is used as the outdoor display screen and advertisement panel and billboard, due to the much more stringent conditions of the operation environment, the light-emitting diode must have sufficiently high withstanding voltage and high electrostatic discharge (ESD) capabilities, so that it can maintain normal, stable, and sustained period of operations, and be able to fully achieve its functions of light-emitting and illumination.
In the following discussion, a general structure and a manufacturing process of the conventional gallium-nitride (GaN) based light-emitting diode will be described.
With reference to FIG. 1 of the attached drawings, the conventional gallium-nitride (GaN) based light-emitting diode 10 comprising: a substrate 11, a buffer layer 12 formed on the substrate 11, an n-type gallium-nitride (GaN) layer 13 formed on the buffer layer 12, a light-emitting stack layer 14 formed on the n-type gallium-nitride (GaN) layer 13, and a p-type gallium-nitride layer 15 formed on the light-emitting stack layer 14.
Dry etching is employed to etch downward through the p-type gallium-nitride layer 15, the light-emitting stack layer 14 and finally reaching the n-type gallium-nitride (GaN) layer 13 to form an N-metal formation region 16.
Afterwards, a transparent conductive layer 17 is formed on the p-type gallium-nitride layer 15, serving as a p-type ohmic contact and being transparent. An N-metal 18, serving as an n-ohmic contact, is formed on the N-metal formation region 16. Welding pads 19 are then formed on the transparent conductive layer 17 and the N-metal 18 respectively.
However, as indicated by the characteristic curve (a) illustrated in FIG. 4 and the characteristic curve (a) of FIG. 5, the values of the reverse withstanding voltage and the electrostatic discharge of the conventional gallium-nitride based light-emitting diode structure are rather too low, which are not high enough to make the light-emitting diode structure sustain long period of high level light emitting and/or illumination performance in the stringent outdoor environment conditions.
Therefore, the purpose of the present invention is to overcome and improve the above-mentioned shortcomings and restrictions of the light-emitting diode of the prior art, so as to achieve the purpose of significantly raise its reverse withstanding voltage and electrostatic discharge, and thus increase its service life.